1. Field of the Invention
The present invention relates to a plastic working method and a plastic working machine for plastically working a plastically workable tube by pressing plastic working tools.
2. Description of the Related Art
Hitherto, a spinning work machine as shown in FIG. 18 has been known as one type of plastic working machines. In FIG. 18, the reference numeral 1 denotes a base and 2 a plastically workable tube, i.e., a workpiece, whose sectional profile is circular.
The reference numeral 3 denotes a chuck for clamping and holding the tube 2 by claws and 4 a tube supporting member fixed to the base 1 to rotably support the tube 2 around the axis of the tube 2. The tube 2 is disposed so that the axial direction of the tube 2 coincides with the longitudinal direction of the base 1 by the chuck 3 and the tube supporting member 4.
The reference numeral 5 denotes a stationary stage fixed via two leg members (one leg member 6 is seen in the figure) fixed on the upper surface of the base 1, 7 a motor for spinning the tube 2 around the axis of the tube 2 (in the direction of so-called Z-axis) and 8 a decelerator fixed on the stationary stage 5 to decelerate the rotation of the motor 7. The motor 7 is attached to the decelerators 8.
The reference numeral 9 denotes a rotary shaft of the decelerator 8, and 10 and 11 bearings fixed on the stationary stage 5 to rotably support the rotary shaft 9 of the decelerator 8. The chuck 3 is attached at the end of the rotary shaft 9 of the decelerator 8.
The reference numerals 12 and 13 denote linear way rails provided in parallel on the upper surface of the base 1 so as to extend in the longitudinal direction of the base 1, i.e., in the axial direction of the tube 2, and 14 a movable stage disposed on the linear way rails 12 and 13 so as to be movable along the linear way rails 12 and 13.
The reference numeral 15 denotes a ball screw provided in parallel with the linear way rails 12 and 13 so as to move the movable stage 14 along the linear way rails 12 and 13, and 16 a motor provided on the upper surface of the base 1 to move the movable stage 14 along the linear way rails 12 and 13 via the ball screw 15.
The reference numerals 17 and 18 denote linear way rails provided in parallel on the upper surface of the movable stage 14 so as to extend in the direction of the width of the base 1, and 19 and 20 movable stages disposed on the linear way rails 17 and 18 so as to be movable independently from each other along the linear way rails 17 and 18.
The reference numeral 21 denotes a ball screw provided in parallel with the linear way rails 17 and 18 so as to move the movable stage 19 along the linear way rails 17 and 18, and 22 a ball screw provided in parallel with the linear way rails 17 and 18 so as to move the movable stage 20 along the linear way rails 17 and 18.
The reference numerals 23 and 24 denote motor mounting members fixed to the movable stage 14, 25 a motor mounted to the motor mounting member 23 to move the movable stage 19 along the linear way rails 17 and 18 via the ball screw 21, and 26 a motor mounted to the motor mounting member 24 to move the movable stage 20 along the linear way rails 17 and 18 via the ball screw 22.
The reference numerals 27 and 28 denote plastic working rolls for plastically working the tube 2 by pressing against the tube 2, and 29 and 30 plastic working roll holding members for holding the plastic working rolls 27 and 28. The plastic working roll holding members 29 and 30 are fixed on the upper surface of the movable stages 19 and 20, respectively.
This spinning work machine is constructed as described above to spin and work the tube 2 by continuously spinning the tube 2 around the axis of the tube 2 and by moving the movable stages 19 and 20 symmetrically in the radial direction of the tube 2 or by moving the movable stage 14 in the axial direction of the tube 2 in the same time and by pressing the plastic working rolls 27 and 28 against the tube 2 while controlling the relative position between the plastic working rolls 27 and 28 and the tube 2. It allows tubular members as shown in FIGS. 19A, 19B, 20A and 20B to be fabricated for example.
However, the primary object of the conventional spinning work machine shown in FIG. 18 is to work the external shape of the tube 2 into a predetermined shape and is not provided with means for controlling the thickness of the tubular member fabricated by the spinning.
Therefore, the plastic deformation mechanism is decided univocally by the predetermined shape and the working process in spinning and working the tube 2 into the predetermined shape. As a result, it has had problems that the thickness of each part of the tubular member fabricated by the spinning work is univocally decided and that a tubular member having a desired thickness at each part cannot be fabricated.
For instance, the conventional spinning work machine has had a problem in fabricating a tubular member having an external shape as shown in FIGS. 19A and 19B that thickness of each part becomes thinner than the thickness before the work and that the part around the bottom of the concave portion indicated by an arrow A is thinned in particular, thus weakening the strength of this part most.
It also has had a problem in fabricating a tubular member having an external shape as shown in FIGS. 20A and 20B that the smaller the sectional area, i.e., the closer to the part where the tube should be shrunk more, the thicker the thickness is and that the thickness cannot be fixed.
The conventional spinning work machine shown in FIG. 18 has had another problem that it is unable to fabricate a tubular member having an axially asymmetrical shape because the tube 2 is spun continuously around the axis of the tube 2.